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March 1985 Marsh-Incubation Temperature and Fish Survival 131 TABLE I.-Analysis of water used for temperature experiments. All units are mg/liter unless otherwise noted. Analysis Well I Well2 Sodium (Na) 231 330 Potassium (K) 4 4 Calcium (Ca) 494 534 Magnesium Mg 202 206 Chloride (Cl) 293 520 Sulfate (S04) 1900 1930 Bicarbonate (HC03) 216 196 Iron, total (Fe) 0.10 0.35 Silica (SiO2) 26.0 26.0 Dissolved Solids 3340 3720 pH (SU) 7.28 7.20 Conductivity (gmhos, 25°C) 3830 4500 Total hardness (CaC03) 2067 2183 Manganese (Mn) ND' ND Copper (Cu) ND ND Zinc (Zn) 0.10 0.10 Nitrate (N03-N) 12.0 11.1 Aluminum (Al) ND ND Silver (Ag) ND ND Mercury (Hg) <0.01 <0.01 Lead (Ph) ND ND Strontium (Sr) 71.6 73.0 'Analyses by the Saline Water Plant, Roswell, New Mexico; 5/1982. 'ND = Not detected. Based largely upon field observations, spawning temperatures have been inferred to be 6-20°C for razorback sucker (Douglas, 1952; McAda and See- thaler, 1975; McAda and Wydoski, 1980), 18-21°C for bonytail and hump- back chubs (USFWS, 1974; Kaeding and Zimmerman, 1983) and 18-23°C for Colorado squawfish (Vanicek and Kramer, 1969; Toney, 1974; Miller et al., 1982). Recent hatchery investigations have demonstrated successful hatching of all four species within a range of about 12-26°C (Toney, 1974; Inslee, 1982; Hamman, 198la-b, 1982a-b; Bulkley et al., 1981). Development time of embryos is inversely related to temperature and survival is reduced at temperatures departing far from 20°C (Hamman, 1982a-b; Bulkley et al., 1981). The present study was undertaken to quantify relationships between incubation temperature and embryo survival of the four fishes. METHODS.-Apparatus.-The experimental apparatus consisted of six 22 liter glass aquaria in which water temperatures near 5, 10, 15, 20, 25 and 30°C were maintained by a combination of cold water inflow and thermostatically-controlled immersion-type heaters. Five aquaria (5-25°C) received continuous inflow of water at approximately 1.0 liter h; the 30° aquarium was static and all tests at that temperature were concluded within 24 hours. Incubation chambers were constructed of 76 mm ID PVC pipe fitted on the bottom with 0.5 mm-mesh nylon netting. Six to eight chambers were suspended in each continuously aerated aquarium. Because microhabitat character- istics of natural spawning sites of these species have not been quantified, it is not known how accurately this experimental system duplicated natural incubation conditions. Water Supply.-Water was obtained from one or both of two wells at Dexter National Fish Hatchery (DNFH), NM. Water from both wells was characterized by relatively high salts (espe- cially sulfate [S04]) nitrate, (NO3-N), and conductivity (Table 1). Ionic species and concentrations are not notably different from those of historic and present-day natural habitats (the Colorado and Gila rivers) of all these fish species at summer flow (USGS, 1926-1980a-b).